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but freshwater can be delivered to the Bay, via the water management system, at
any time. During extreme rainfall events, large volumes of water can be released
over very short periods of time. Low salinity, poor quality water that is delivered
in this manner may not mix well with surrounding higher salinity water and
may persist for long periods of time (Brook 1982, Szmant 1997, Serafy et al. 1997).
Other problems occur due to reduction of freshwater flows during the dry
Biscayne Bay Characteristics
Freshwater Flow and Ecological Relationships in Biscayne Bay 2-13
season and droughts. High demands for water, to meet urban and agricultural
needs, result in discharges of water from the regional system during the dry
season to protect coastal well fields.
Watershed land use changes have resulted in concurrent changes to the water
quality of the surface and groundwater flows to Biscayne Bay. Although overall
water quality in Biscayne Bay has improved in recent years (Alleman et al 1995),
water quality is still a substantial concern in the watershed. Water quality ranges
from severely degraded in the Miami River to very good near the Featherbed
Banks (Alleman et al 1995). The 1995 Biscayne Bay SWIM Plan reports the trend
analysis for a variety of constituents.
EXISTING SPECIES AND ECOLOGICAL CONDITIONS
In its + 57 mile length, Biscayne Bay varies considerably in physical conditions.
From its narrow northerly extreme, the Bay widens to a maximum width of over
seven miles in the south-central region. Flora and faunal communities vary
considerably throughout the Bay, and are generally determined by a variety of
environmental factors and physical characteristics (e.g., water depths, water
quality, extent of tidal exchange with the ocean), some of which are fairly static,
others of which are very dynamic. As a result of these varying conditions,
benthic and epibenthic habitats vary considerably. In some areas, ecologically
valuable seagrasses are present in lush grassbeds. In other areas, seagrasses are
absent, or are interspersed with macroalgae and/or hardbottom. Since 1966,
over 512 species of fishes have been documented to occur within Biscayne Bay
(R. Alleman, pers. comm.).
In addition to the salinity-related variability described above, other water quality
parameters also vary considerably in different areas of Biscayne Bay. In some
eastern areas, the absence of barrier islands that would restrict tidal exchange,
create marine conditions which provide habitat for a wide diversity of naturallyoccurring sub-tropical floral and faunal assemblages.
In other areas, due to a combination of factors, including the presence of barrier
islands that reduce tidal exchange with the Atlantic Ocean and significant
destruction of naturally-occurring shoreline communities, water quality is
comparatively poor and species richness, abundance, distribution and health is
considerably reduced.
Although conditions in a natural, unaltered Biscayne Bay would be highly
variable, human-related changes in the recent past (i.e., + 100-150 years) have
significantly altered the Bay. These changes, which have included construction
of tidal inlets, replacement of mangrove shorelines with seawalls and bulkheads,
Biscayne Bay Characteristics
Freshwater Flow and Ecological Relationships in Biscayne Bay 2-14
and dredging of shallow bay bottoms to create navigation channels, marinas, and
deep-water ports have resulted in Biscayne Bay being in a highly modified
condition. In general, these activities have had adverse impacts on the
environmental value and quality of the Bay, but it some areas, the creation of
new and/or different habitats than what had previously existed may have
resulted in increased biodiversity.
Although the floral and faunal assemblages at any given site may be
considerably different than at other sites, the species that are present are largely
the result of the combination of available habitat and ambient water quality.
Some species that are tolerant of extremely variable conditions are likely present
throughout the entire Bay. Other species may be restricted to certain areas based
upon their individual habitat requirements. As described in Sections 2.a-c
above, for the purposes of establishing a rule for Minimum Flows and Levels,
Biscayne Bay has been separated into six distinct sub-regions. In the remainder
of this section, information is provided about the ecological conditions and/or
notable species that are present in each of the sub-regions.
Snake Creek/Oleta River Sub-region
In addition to Snake Creek and the Oleta River, this northern-most sub-region of
Biscayne Bay also includes Dumfoundling Bay, Maule Lake and Oleta River State
Park.
There are no direct surface water connections between these waters and the
Atlantic Ocean within this sub-region, although Haulover Inlet is a short distance
to the south. Prior to the opening of Haulover Inlet during the 1920s, this area
was primarily a freshwater system (FDEP, 2002). Much of the historic shoreline
has been altered, and previously existing native vegetation has been replaced
with seawalls and bulkheads. An exception to this, however, is the + 1043-acre
Oleta River State Park, which is located on the west side of the Bay, immediately
south of S.R. 826. The most extensive current ecological information that is
available for this region is the Unit Management Plan for Oleta River State Park
(FDEP 2002) The Management Plan identifies and describes the four vegetative
communities that exist within the park, including: beach dune, maritime
hammock, estuarine tidal swamp and estuarine unconsolidated substrate, in
addition to ruderal/disturbed and developed areas. Floral and faunal
inventories conducted within the state park have documented the presence of
approximately 290 species of plants and 95 animal species, consisting of six
species of invertebrates, nine species of fish, one amphibian, ten reptiles, 59
species of birds and ten species of mammals.
Biscayne Bay Characteristics
Freshwater Flow and Ecological Relationships in Biscayne Bay 2-15
Eighteen plant species that are designated as threatened or endangered by the
State of Florida are present within the park, none of which designated as
threatened or endangered by the federal government. Only one of these species,
golden leather fern (Acrostichum aureum) is an emergent wetland-related species.
The typical habitat for this herbaceous species is the low-salinity muck soils
along the Oleta River. Johnson’s seagrass, a submerged species that is
designated as ‘threatened’ by the federal government, is present in shallow
waters in this sub-region of the Bay. Submerged lands within this sub-region
from S.R. 826 southward to the south boundary of this sub-region have been
designated as critical habitat for Johnson’s seagrass (Figure 8).
Twelve animal species that are listed as endangered, threatened, or species of
special concern by the state are known to exist within the state park. Three of
these, (i.e., bald eagle, wood stork, and West Indian Manatee) are also listed as
threatened or endangered by the federal government. Several of the designated
species are species that forage in, or otherwise inhabit coastal areas. These